Unlock Seamless Multi-Format File Previews with kkFileView

Project Overview

File Online Preview (kkFileView) is an open‑source service built on Spring Boot that offers RESTful APIs for cross‑language, cross‑platform file preview. It can be integrated into Java, PHP, Python, Go, and other applications.

Project repository: https://gitee.com/kekingcn/file-online-preview

Core Features & Technical Highlights

1. Rich File Format Support

The project supports more than 100 file formats, covering:

Text files: txt, html, htm, asp, jsp, xml, json, md, log, java, py, c, cpp, sql, sh, bat

Image files: jpg, jpeg, png, gif, bmp, ico, webp

Office documents: doc, docx, xls, xlsx, ppt, pptx, csv, tsv, pages

PDF documents: pdf, ofd, rtf

Archive files: zip, rar, jar, tar, gzip, 7z

Media files: mp3, wav, mp4, avi, mov, mkv, webm, ogg

CAD drawings: dwg, dxf, stl, ifc

3D models: obj, 3ds, gltf, glb, stl, ply, fbx

Special formats: eml, epub, xmind, bpmn, dcm, drawio

2. Sophisticated Technical Implementation

File Preview Architecture

The system uses a "convert + render" two‑layer architecture.

File reception & identification: REST API receives a file URL and determines type by extension.

Intelligent conversion processing:

Office documents: OpenOffice/LibreOffice API converts to PDF.

PDF documents: PDF.js parses directly.

CAD drawings: Dedicated tools (e.g., AutoCAD) generate preview images.

3D models: Browser‑side rendering with Three.js.

Efficient caching: Conversion results are stored in Redis or local cache.

Front‑end rendering: PDF.js, FlexPaper, etc., provide smooth preview.

Performance Optimization Strategies

Asynchronous processing via Spring Boot @Async.

Paginated preview for large documents.

Memory management with chunked processing.

Cache keys based on file content hash.

Compressed transmission of converted files.

Security Mechanisms

File type whitelist.

Access permission validation.

Integrated virus scanning.

HTTPS and content encryption.

Rate limiting to prevent abuse.

Project Architecture & Tech Stack

Core framework: Spring Boot 2.7.x (Java 11).

Dependencies: OpenOffice/LibreOffice, Redis (optional), specialized conversion tools (AutoCAD, Blender, etc.).

Front‑end technologies: PDF.js, Three.js, FlexPaper.

Implementation Details

1. Office Document Conversion

Conversion is performed via the OpenOffice API. Key code:

public String convertToPdf(String fileUrl) {
    // 1. Download file to temporary directory
    File tempFile = downloadFile(fileUrl);

    // 2. Start OpenOffice service
    LibreOfficeConverter converter = new LibreOfficeConverter();

    // 3. Convert document to PDF
    File pdfFile = converter.convert(tempFile, OutputFormat.PDF);

    // 4. Return PDF path
    return pdfFile.getAbsolutePath();
}

2. Encrypted PDF Preview

Handles encrypted PDFs using iText:

public String previewEncryptedPdf(String encryptedFileUrl, String password) {
    // 1. Download encrypted file
    File encryptedFile = downloadFile(encryptedFileUrl);

    // 2. Use iText to process encryption
    PdfReader reader = new PdfReader(encryptedFile, password.getBytes());

    // 3. Create temporary decrypted file
    File decryptedFile = new File(System.getProperty("java.io.tmpdir"), "decrypted_" + UUID.randomUUID() + ".pdf");
    PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(decryptedFile));
    stamper.close();

    // 4. Return preview URL of decrypted file
    return fileService.uploadFile(decryptedFile);
}

3. 3D Model Browser Rendering

Front‑end rendering with Three.js:

function load3DModel(modelUrl) {
    const loader = new THREE.GLTFLoader();
    loader.load(modelUrl, function(gltf) {
        scene.add(gltf.scene);
        // Set camera and lighting
        camera.position.z = 5;
        renderer.render(scene, camera);
    });
}

Project Advantages

Comprehensive functionality: supports 100+ formats.

Easy deployment: Spring Boot application can be started in three steps.

Excellent performance: multi‑layer optimizations ensure stability under high concurrency.

Secure and reliable: built‑in security mechanisms protect files.

Active iteration: latest v4.4.0 adds medical image (dcm) and drawio preview.

Quick Integration Guide

1. Local Deployment

# Clone the project
git clone https://github.com/kekingcn/file-online-preview.git

# Enter project directory
cd file-online-preview

# Run the service
mvn spring-boot:run

2. API Call Example

GET /file/preview?fileUrl=https://example.com/document.pdf

3. Response Example

{
  "code": 200,
  "data": {
    "previewUrl": "http://your-server:8012/preview/file/12345.pdf",
    "fileType": "pdf",
    "isEncrypted": false
  }
}

Applicable Scenarios

Enterprise document management systems.

Cloud storage services.

Online education platforms.

E‑government portals.

Collaboration office software.

Conclusion

File Online Preview (kkFileView) offers a full‑stack, high‑performance, secure solution for file preview across a wide range of formats, making it a top choice for enterprise‑level applications. Its open‑source nature and active community further empower developers to build high‑quality solutions.

Project continues to evolve with new features such as DCM medical image preview, drawio diagram preview, and encrypted PDF preview.